In this picture the moon is seen illuminated solely by light reflected from the Earth. NASA Planetary Photojournal

A meteoroid “the size of a small boulder” crashed into the moon causing the biggest explosion that NASA has ever observed since 2005.

“It exploded in a flash that is ten times brighter than anything that we have ever seen before,” said Bill Cooke of NASA’s Meteorite Environment Office.

Ron Suggs, analyst at the Marshall Space Flight Center, was the first to notice the impact in a digital video recorded using a 14-inch telescope. The meteoroid weighed less than 100 pounds and was less than 1.5 feet wide. It speed of impact at 56,000 miles per hour caused a giant explosion equivalent to 5 tons of TNT.

“For about one second the impact site was glowing like a fourth magnitude star,” said Cooke, who believes the impact could belong to a much larger event. For the past eight years, NASA astronomers have been observing signs of meteor showers on lunar surface, which occurred more frequently than expected. Hundreds of impact have been detected in the last eight years.

“On March 17th, NASA and University of Ontario All-Sky Cameras picked up an unusual number of deep penetrating meteors right here on earth,” he said.

“They were traveling at nearly identical orbits between earth and the asteroid belt. This means that the earth and the moon were pelted by asteroids at the same time. My working hypothesis is that the two events were related and that this constitutes a short duration cluster of material encountered by the earth-moon systems,” says Cooke.

This meteoroid crash was part of a larger meteoroid event as NASA also detecting a spike in meteoroids entering Earth’s atmosphere. Earth’s atmosphere tends to burn up the space debris. The moon has no such protective layer.

Unlike Earth, the moon has no atmosphere to protect it. As there is no oxygen, it poses the question of how they explode.

“Lunar meteors don't require oxygen or combustion to make themselves visible. They hit the ground with so much kinetic energy that even a pebble can make a crater several feet wide. The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site,” NASA explains.

U.S. space exploration policies eventually call for extended astronaut stays on the lunar surface. Identifying the sources of lunar meteor and measuring their impact rate give further lunar explorers an idea what to expect.

Cooke said, “We’ll be keeping an eye out next year when the earth-moon system passes through the same region of space. Meanwhile, our analysis of the March 17th event will continue.”